Rd400 more low / mid?

[rd400canuck]

I'd like to do what I can to get more low end grunt on this RD400c. I had a 1980 RD400G for a few years and it was so torquey in the low/mid I loved it so much for driving around town.

The only thing I can think of is correct the squish. If I'm correct that will add power mostly to low mid ? I have all stock intake track and stock exhausts.

Any other tricks?

[m in sc]

is the carb tuning dead stock? have the carbs been taken apart and the brass ball drilled out and cleaned behind(air jet)? if not, start there. 

[rd400canuck]

I havent actually built the motor yet. I bought the bike couple weeks ago and it was running like crap. Once I had a look at the hack job on the cylinder ports and one of the carbs was missing the main jet washer I knew it made no sense to try and tune it until I replaced the cylinders and reworked the carbs.

I have ordered stock 175-P2's and 115 mains and 25 pilots all mikuni stuff. The 5L1 needles look fine.  That's what's in the carbs now but I wanted everything new and clean.

I'm praying and hoping that if I put everything to stock... I wont run into jetting nightmare. The only thing that wont be stock will be the cyclinders at 1mm over. All porting will be stock and untouched as well.

[m in sc]

yeah should be good to go.

[Dvsrd]

I was under the impression that the later 400s had less exhaust port duration than the earlier models. And were torquier/less revvy. Or was that just the US Daytona?

[rd400canuck]

looks like it was just the Daytona to me

http://erlenbachracing.co/portmaps.htm

So it seems the porting I had on my 400G is very close the the RD400c I have now..  If they run similar and have to same low / mid power I will be happy. The Daytona must be awesome in the city with that porting. These bikes arent any fun, for me, when they are so tuned and piped that they literally make almost no power until 6000 rpm then it pulled hard. Almost a literal light switch power band.

The RD400G had DG's on it and a 2 into 1 filter set up. I HATED that bike... had to rev the freaking snot out of it just to take off from a light, was ridiculous. Went apeshit after 7000 rpm but so what? The bike would only be good on a track like that.

The intake drone was killig me so I went a found stock airbox setup and after tuning carbs I could not believe how much better the bike was. i was really shocked because I had spent years with this bike and couldnt stand the power. After that I scored some stock pipes and rejetted...  again I was shocked what a wonderful torquey bike this turned into. I learned my lesson after that with these old two strokes to keep them stock for the kind of relaxed riding I do. Plus I adore the stock pipe's sound. Just so much more of a pleasure to ride.

[Organicjedi]

Dropping a tooth on the front sprocket would help. Could do a 520 chain conversion while you're at it.

I'm very happy with the Stg 1+ job that Supertune Chuck did for me. That plus the pipes and the down geared final drive along with the modded carbs and Vforce reeds really improved low/mids. The bike pulls very hard off the line and just keeps going.... all depends on how far you want to go.

[rd400canuck]

Here's the bike I just bought in Toronto. Going to spend the winter rebuilding it.

[rd400canuck]

Dropping a tooth on the front sprocket would help. Could do a 520 chain conversion while you're at it.

I'm very happy with the Stg 1+ job that Supertune Chuck did for me. That plus the pipes and the down geared final drive along with the modded carbs and Vforce reeds really improved low/mids. The bike pulls very hard off the line and just keeps going.... all depends on how far you want to go.

I am going to keep it as stock as I possibly can. I'm so afraid to go down that rabbit hole after the 2 RZ350's and the RD400G I had. My tuning days are over!

The only thing I would change is to an electronic ignition and maybe get the squish corrected to 1mm. That's about as far as I'm willing to go. I think with how short the gears are already going down a tooth in the front isnt in the plans. I'll stick to stock. I guess my aim is to make the bike comfortable for bombing around town without too much effort.

[2steve]

Higher compression heads seems like a good move.
I'm so very pleased with the added grunt of having found some cheap heads that had been doctored and Chuck's update porting job - which is also great for stock pipes. He doesn't change port timing, just makes your engine a more efficient "pump."
Might need some tuning tweaks though.

[rd400canuck]

I'm curious now.... Does Chuck have a website?

[pdxjim]

The Kawasaki Triples guys claim that adding +/- 4" intake runners between the pods and carbs (basically like a y-boot in theory) helps bring back some of the low-midrage that is lost when ditching the stock airbox.

It did seem to help with rideability on my KH400, but not sure how much this translates to a reed valve motor, as the KH is piston port.

[rd400canuck]

I guess I could try a reed spacer but there isnt much room there with the stock airbox which I definitely want to keep. I'm not a fan of intake noise... plus after installing the airbox into my RD400G and seeing how it transformed that bike I've come to realize those Yamaha engineers knew what they were doing.

I think it looks like my only real choice for improved bottom/mid is to get that head shaved. I think economycycle pins the heads for that. After I get the bike running perfectly I'll see about getting the squish corrected.

[rd400canuck]

Is the 520 chain conversion so that they can run o-ring chains?

[pdxjim]

Is the 520 chain conversion so that they can run o-ring chains?

520 chain is lighter than the stock 530.  In theory, the heavy overkill 530 stock chain robs some power.